1. Field of the Invention
The invention relates to a connecting piece for a line or an apparatus to be screwed therein to provide a closed pressure-fluid circuit, said connecting piece comprising a hollow many-sided head and a hollow-screw with a thread, said hollow screw being in one piece with said hollow many-sided head.
2. Description of the Prior Art
It is known to use varnishes, pastes, putties, fibres, foil strips, taper threads and sealing rings as sealing means to eliminate the pressure losses between the connecting pieces and the respective parts to be connected together by these connecting pieces. The pressure flowing in the circuit is either a pressure liquid or a pressure gas.
The first five sealing means can impair the function of the lines or the apparatuses when they get into the inside of these parts. Taper threads often destroy the apparatus or line portions by means of their wedge effect. When the sealing rings are squeezed only a little too powerfully, they burst or they are dislocated from the wanted position. The inappropriate deformation of the sealing ring by the tightening of the connecting piece causes a premature aging of the sealing ring by means of which the sealing efficiency of the same is reduced or is practically zero.
All the known above described connecting systems have a common disadvantage that the sealing means have to be renewed in each case when the connecting piece is reused.
It is further known from a proposal to an international standard ISO/DIS 6149 that a sealing ring is inserted between the connecting piece and the part to be connected in such a way that it abuts on one side against the wall of the thread end of the screw running parallel with the longitudinal axis of the connecting piece and on the other hand against a wall of the part to be connected running conically outwardly from the longitudinal axis of the connecting piece.
In this case the forces act against the wall running parallel with the longitudinal axis of the connecting piece. This wall will be deformed in the perpendicular direction to the longitudinal axis of the connecting piece in a short time.
The screw of the connecting piece has a gate at the thread end (in the proximity of the many-sided head) which gate is implied by the instrument in the course of cutting the thread.
It is known to cut a circular recess for a sealing ring into an angle formed by the thread end and the bottom surface of the many-sided head, which recess is inclined in 45.degree. to the longitudinal axis of the connecting piece. Such a recess has, however, an edge formed by an obtuse angle which is the source of damage of the sealing ring when it is inserted into the circular recess.
It is further known to provide a circular recess in the bottom surface of the many-sided head in such a way that the gate at the thread end will not be cut, but a circular recess will be cut only in the bottom surface of the many-sided head away from the thread end of the screw. However, when the sealing ring is not optimally dimensioned to suit the overall dimensions of the circular recess, the metal part of the many-sided head and the metal of the part to be connected can not be brought to lie on each other and the sealing ring introduced into such a circular recess will be so heavily deformed that it will be soon destroyed. Besides, in such a case the sealing ring can be injured by the edge of the circular recess, when it is inserted into the same. The mounting of the sealing ring into such a recess is difficult.